The present invention relates to a file unit for a magnetic disk unit, an optical disk unit, etc., and more particularly, to a parallel transfer type (or a multi-channel type) disk unit for simultaneously recording and reproducing with heads mounted on a plurality of driving units.
Usually, a plurality of magnetic heads 520, 521, 522 and 523 are mounted on one driving unit (a head transfer mechanism) 510 in a magnetic disk unit, and one of these magnetic heads is selected to record on and reproduce from a disk 530, as shown in FIG. 1. On the other hand, parallel transfer type magnetic disk units have been proposed for recording and reproducing information on and from tracks by parallel splitting of the information, after it is converted from serial data to parallel data, onto parts of about one bit or one byte, and by simultaneously operating recordable and reproducable magnetic heads as pairs without operating a transfer mechanism (such as heads 520 and 521 of which state is described in Japanese Patent Unexamined Publication No. JP-A-54-39611, and heads 521, 522, 523, . . . , of which state is described in Japanese Patent Unexamined Publication No. JP-A-61-145767). 511 designates a head driving voice coil motor and 512 designates a carriage.
A parallel transfer type file system is disclosed in the Mini-Micro systems, December 1987 edition, pp. 15-16. This system takes a rotation synchronization between a plurality of disk units to parallel transfer data.
The above-described techniques aim at obtaining a high data transfer speed by dividing a data recording at one position and simultaneously recording and reproducing the data.
In a magnetic disk unit, a magnetic disk is inspected when the unit is shipped. A track having many large defects is judged to be incapable of recording or reproducing data, and is registered initially as a defective track. Registration of a defective track is recorded in a home address section 635 which immediately follows an index marker 634 of each track in the track format shown in FIG. 2. Use of a defective track is inhibited and another track is designated as an alternate track. A position of the alternate track is indicated by a record R.sub.0 636 of a 0-th position following the home address section. A record 1 (637) to a record n is an area which a user can use, where n changes depending on a record length of a user data.
A structure of the above format is described, for example, in the IBM JOURNAL OF RESEARCH AND DEVELOPMENT, November 1974 edition, pp. 489-505.
A specific position near the inner most periphery is usually a convenient position for the above-described indicated alternate track. According to the conventional unit, when there is a defective track in a group of tracks which are transferred in parallel and when a replacement track is indicated, a group of good tracks are recorded first and then a head is repositioned to the alternate track and data is sent again from the computer and recorded on the replacement track. At the time of reproduction, the original track (a good track) is reproduced and then the replacement track is newly reproduced and data is sent to a controller a plurality of times (for the good track and the replacement track). This means that it takes twice the number of moves of a head between the defective track and the alternate track for the data transfer. Therefore, the total throughput of the file system is reduced by the conventional method.